Method for producing curved laminated structures



Apnl 1, 1947. v. E. WATTS METHOD FOR PRODUCING CURVED LAMINATED STRUCTURES 2 Sheets-Sheet 1 Filed Nov. 17,1944

Ii'las Lllhlis v. E. WATTS 2,418,433

METHOD FOR PRODUCING CURVED LAMINATED STRUCTURES Fi1ed Nov. 17, 1944 zsneezs-sna ex 2 Iilasl? Walls Patented Apr. 1, 1947 UNITED STATES) PATENT OFFICE METHOD FOR PR DUCING CURVED LAMINATED STRUCTURES This invention relates to a method for producing curved laminated structures. More particularly, the invention contemplates a method for the production of curved laminated plywood to marine, aircraft, silo, and like constructions.

It is an object of the invention to provide a practical effective method for producing curved. laminated structures without necessitating the for use in carrying out the method of the invention; and r Fig. 6 illustrates still a further modified form of assembly capable of employment in carrying structures of great extent such as are applicable out the method of the invention.

While the method will be described in relationship to the accompanying drawings, it is to be understood that the drawings are by way of exemplification only and that; the form and curvaemployment of expensive cumbersome equipture of the laminated structure may vary mament.

It is a specific object of the invention to' provide a method for producing curved laminated structures embracinga plurality of plies having terially from that illustrated The first step in the method resides in the provision of a suitable base form, non-deformable under the conditions of operation and having a adhesive interposed between opposing urfaces. is curved surface configuration conforming to the of the plies without the use of presses, platens,- and like instrumentalities.

More specifically, it is the object of the invention to provide a method embracing the prodesired curvature of the laminated structure to be produced.

In Fig. 1, the non-deformable base form is illustrated generally at I0, and in this instance vision of a base form d f b1 under the is shownas being constructed of concrete, though conditions of operation. having a curved surface configuration conforming to that of the desired laminated structure, the building up of plies with intervening layers of heat-sensitive adhesive such it may be of any suitable material and construction o long as it is non-deformable under the conditions of operation and partakes of a curved surface conforming to that of the desired lamias phenolic resin on the base form, applying heat Hated Structure and pressure to successive segments of the laminated structure on the curved surface thereof through the medium of a fluid-containing flexible bag, and so conducting the steps of the process as to preclude application of heat without pressure to areas of the structure that would be damaged thereby.

This application is a continuation-in-part of my copending application Serial Number 373,138 filed January 4, 1941.

Other and more detailed objects of the invention will become apparentas the description of the method proceeds, which will be given in connection with the accompanying drawings forming a part of this application and in which:

Fig. 1 i a perspective view illustrating an assembly embracing an extended curved laminated structure being fabricated in accordance with the invention;

Fig. 2 is a view showing in more detail certain elements of the assembly of Fig. 1;

Fig. 3 is a sectional view along the line 3-3 of Fig. 1, and additionally illustrating in dotted lines the stepwise progression of the method;

g. 4 is a detailed View of one form of flexible fluid-containing bag adapted for use as an element of the assembly employed in carrying out the method;

Fig. 5 illustrates a modified assembly adapted 55 The next step in the, process embraces the building up on the non-deformable base'form ill of the plies indicated at H, l2 and I3 oi the laminated structure, with interposed layers of a heat- 30 sensitive adhesive which may be either thermoplastic or thermosetting, the whole being capable of being permanently bonded or cemented as a unitary structure by the" requisite application of heat and pressure.

T e next step in the process embraces the step- Wis; application of the requisite heat and pressure to permanently cement and bond the laminated structure, while in place on the non-deformable base foim- III. This step of the process is carried out by applying the requisite heat and pressure, first "to an initial segment such as seg-,

ment A (Fig. 1) on the curved surface of the laminated structure indicated generally at [4,

through the medium of a fluid-containing flex ible bag "l5 restrained to the contour of the segment A through the medium of suitable restraining straps I6, which may be of steel or other appropriate non-extensible material, and the flexible reinforcing member I! lying between the 'straps l6 and the bag I5.

In the exemplified embodiment of the invention, therestraining straps l6 are adapted to be locked in restraining position by the pins [8 carried by the non-deformable base form ID. The heat-and-pressure applying assembly is shown in Fig. 1 at an intermediate stage in the stepwise progression along the extended curved laminated structure, it being understood that segments A and B of that structure are indicated as having already been cemented, with segment C shown as being under treatment.

The stepwise manner of, progression is well I .heated fluid circulating under the requisite pressure through section I9 of the bag I5. The applied heat is prevented from creeping to adjacent areas of previously treated segment B and unillustrated in Fig. 3, wherein the flexible bag I5, shown in full lines, is shown with the heat-andbonding of the piles of the curved laminated "structure I4 by the heat-sensitive adhesive be uniform throughout the extent of the curved laminated structure. It is a feature of the present invention that in the stepwise progressive application of heat and pressure to successive segments of the curved laminated structure, there will be no creeping of heat While being applied to one segment to the area of an adjacent segment not under pressure and where such heat would have a deleterious effect upon the bonding medium.

In carrying out the method, provision is therefore made to preclude the creeping of heat applied to one segment to adjacent areas not under pressure. With the assembly exemplified in Figs. 1 to 4 of the drawings, this is achieved by providing heat absorbing sections within the fluidcontaimng flexible bag I5. These marginal heat absorbing sections are shown at and 2| in Figs. 3 and 4. Pressure is applied to a selected segment of the laminated structure I4 through the medium of the flexible bag I5 by circulating fluid under the required pressure through the expansible flexible bag I5 restrained to the contour of such segment.

Pressure is applied throughout the width of the flexible bag I5, but heat is applied only throughout the width of the heat applying section I9 to which fluid under the requisite heat and pressure is supplied by line 22 and header 23, which fluid is discharged at the opposite end of heateand-pressure applying section I9 of bag I5 through line 24 and header 25, as shown in Fi 2.

It will be understood that lines 22 and 24 are connected into a closed cycle provided with an appropriate circulating pump and heat restoring instrumentalities not shown. It will also be understood that the fluid circulated through the heat-and-pressure applying section I9 of the bag I5 will be a fluid that is appropriate for the purpose.

Heat absorbing pressure applying fluid is circulated through the marginal heat absorbing pressure applying sections 20 and 2I of the bag I5, by being supplied thereto through the line 26 and header 21, the fluid discharging from the opposite ends of the heat absorbing pressure applying marginal sections 20 and 2| of the bag I5 through the line 28 and header 29, shown in Fig. 2, and may be circulated in a closed cycle (not shown). I

With the assembly in the position shown in Fig. 1, wherein, the heat-and-pressure applying section I9 of the bag I5 overlies the segment C of the curved laminated structure I4, the requisite heat and pressure for bonding the heat-sensitive adhesive is applied to the segment C by the applied or is yet to be applied.

treated segment D by the cold heat absorbing pressure applying fluid circulated through the marginal sections 20 and 2| of the bag I5.

When a given segment such as segment C of Fig. 1 has been subjected to the requisite heat and pressure for a time interval appropriate to satisfy the requirements of the particular heat-sensitive adhesive employed, the elements of the assembly embracing the bag I5, the reinforcing member I1, and the restraining straps I6, are advanced to the next adjacent segment, as ,for example D in Fig. 1, and the operation repeated. This stepwise progression is continued until the entire structure has been cemented through application of the requiste heat and pressure. The fluid circulated through the marginal chambers 20 and 2| will be under the same pressure as the fluid circulated through the intermediate heat-and-pressure applyingzone I9. However, the fluid moving through the marginal chambers 20 and 2| will be cold and will absorb and dissipate any tendency of the heat to creep from the segment such as C, to which heat and pressure is being applied to adjacent segments, to which heat and pressure has either already been The particular manner 0;

adhesive employed as the bonding agent for the plies of the curved laminated structure I4 is thermosetting or thermoplastic. For example, where the adhesive is thermosetting so that the heating of as yet uncemented surface not under pressure would be deleterious, the cold fluid needonly be circulated through the marginal chamher on that s de of thebag I5 adjacent the as yet uncemented area of the curved laminated structure.

On the other hand, when the adhesive is thermoplastigs'o that th re-heating of an area that has already been cemented and is not under pressur would be deleterious, it is to be understood that the cold fluid will be circulated through the marginal chamber on that side of the bag I5 adjacent an already treatedand cemented segment. f"

The method is suscefiible of being practice-d through other instrumentalities than those specifically illustrated in Figs. 1 to 4 of the drawings; and a different form of assembly is illustrated in Figs. 5 and 6.

Referring to Fig. 5, laminated structure I4 on the non-deformable base I0 is adapted to have applied to a given segment thereof, such as C, a. flexible electric heating pad 30 having appropriate wiring connections 3!. This flexible heating pad 30'has'dimensions conforming to the extent of the segment of th curved surface of the laminated structure desired to be treated in one step. An insulating pad 32 is adapted to overlie the heat ng pad 30, and is of the same dimensions as the pad 30. A flexible fluid-containing bag 33 is adapted to be placed over the pads 30 and 32, and as shown in Fig. 5 to extend a substantial distance beyond one side of the pads 30 and 32 as indicated at 34. A reinforcing flexible member 35, similar to the reinforcing flexible member I1, overlies the bag 33 and the restraining straps 36 are comparable to and per-. form the same function as the restraining straps I6 of Fig. 1.

conducting the method will depend somewhat on whether the It will be observed that the bag 33 is not subdivided into sections, but has a unitary fiuidcontaining chamber coextensive with the dimensions of the bag. In the employment of this assembly, it is unnecessary to provide a heated circulating fluid, Cold fluid only is circulated through the bag 33 under the requisite pressure to meet the requirements of the particular heatsensitive adhes v being employed. The heat is applied through the electrical heating pad 30. That portion of the bag 33 which extends beyond the side of the pads 30 and 32 acts to provide a heat absorption area so that any heat tending to creep from the section C is absorbed by the cold fluid circulating through th bag 33.

The assembly as shown in Fig. 6 is the same as shown in Fig. 5, with the exception that the bag 33 extends beyond the heating pads 30 and 32 at both marginal edges thereof, as indicated at 34 and 3'l in Fig. 6, In this way, a pressure applying heat absorbing area is provided on both sides of the heat applying instrumentality in the form of the electrical heating pad 30.

It will be understood that in employing the assemblies of Figs. 5 and 6, the stepwise progression will be the same as has been hereinbefore described in respect to th assembly of Figs. 1 to 4.

Generally speaking, it is desirable to use heat polymerizable synthetic resin which, when polymerized is water insoluble, infusible, and chemically inert, as the heat-sensitive adhesive, particularly in the fabrication of laminated marine structures and the lke. Resins suitable for use in carrying out the methods of the invention embrace the water-solubl phenolic l quid resins, concentrated urea resins, alcohol soluble phenolic resins, and dry phenolic resin films which may consist of tissue-thin paper impregnated with a phenolic resin.

The pressures required for effecting the proper bonding of the plies of the lamnated structure will depend somewhat upon the particular character of the heat-sensitive adhesive employed, but will usually run in the neighborhood of from to '350'pounds per square inch. The temperature will likewise vary depending upon the character of the heat-sensitive adhesive employed, but will usually not exceed 350 F. The time required for effectively bond ng and cementing the plies of the curved laminated structure in a given segment may also vary somewhat depending not only on the character of the heat-sensitive adhesive but also upon the number of plies and the thickness of the over-all laminated structure. By way of example for a curved laminated structure having a total thickness of approximately five-eighths of an inch and employing a liquid phenol c resin, known commercially as "Bakelite resin X-C-1148, the time interval for the heat and pressure treatment of each segment will be approximately ten minutes.

It will be understood that in building up the plies II, I2 and I3 0n the non-deformable base It), the different plies will be arranged with the grain of the wood in alternate layers extending in different directions so as to give an over-all rugged construction. The different sections of the plies need not be accurately planed to uniform thickness, since one'of the great advantages of the instant invention resides in the fact that the uniform application of pressure is obtained through out the area of a given segment treated, irrespective of irregularities in the surface and the thickness of the various elements of the respective plies. This is a result that cannot be achieved by ordinary pla'ten rolls or presses, and it is highly advantageous, particularly in the production of extensive curved laminated structures for such exacting uses as marine hulls and aircraft wings.

It is to be understood that the foregoing description is by way of exemplification of the invention, and is not to be construed in limitation thereof, the scope of the invention being that of the subjoined claim.

Having thus described my invention, what I claim is:

A method for producing curved laminar structures of large dimensions and irregular contours containing adhesive between the opposing surfaces of the plies, comprising initially providing a stationary pressure-resisting form having a curvilinear surface of large area conforming to the desired curvilinear contour of the laminated structure to be produced, building up on said form a laminated structure embracing a plurality of plies with interposed layers of adhesive, applying pressure to all of a predetermined segment of the curved surface of said structure in a direction normal to said curved surface at all points thereof by fluid under pressure, applying heat to an intermediate part only of said segment, precluding the application of heat to that marginal part of said segment of the curved surface adjacent to the area of said structure which is not under pressure to prevent application of heat without pressure to areas of the structure that would be damaged by such heat, and repeating the application of heat and fluid pressure in the same manner to succeeding adjacent segments until all of the J curved laminar structure has been cemented.

' VILAS E. WATTS.

REFERENCES CITED The following references are of record lnthe 

